There has long been a need to employ catalysts in reactions such as simultaneous combustion of carbon monoxide, unburned hydrocarbons and the reduction of nitrogen oxides (NOx) which are emitted from automotive engines and the like. The role of catalysts, particularly three-way catalysts, in automotive emission control has been widely studied in the art. For example, Taylor, "Automobile Catalytic Converter", Catalysis, Science and Technology, pp. 119-67 (Anderson et al. eds. 1984), describes emission control technology, composition of three-way catalysts, and catalytic supports.
Conventional systems for converting automotive exhaust gases employ a pre-fabricated supported catalyst, typically a solid stratum of catalyst material, such as honeycombed ceramic structures, which are placed in the exhaust section of the automobile. As the emissions pass through the solid, the catalytic metal present on the strata aids in conversion of CO, NOx and unburned hydrocarbons to CO.sub.2, N.sub.2 and H.sub.2 O. However, the solid strata-type catalytic converter eventually become spent, and require removal and replacement in the exhaust portion of the engine. Moreover, structures such as a honeycomb support are complex and relatively expensive to manufacture. State of the art systems capable of carrying out three-way catalysis include those having supported noble metals such as rhodium and platinum metals, with rhodium being a preferred catalyst for the reaction: EQU NO+CO.fwdarw.1/2N.sub.2 +CO.sub.2
Platinum is the preferred catalyst for oxidation of CO and unburned hydrocarbons.
The noble metals are expensive and in limited supply, particularly rhodium. This situation is exacerbated by the fact that current usage of platinum and rhodium in three-way catalysis exceeds the mine ratio of Rh/Pt. Thus, reduction of noble metal usage is a problem in three-way catalysis. Therefore, it is necessary to develop alternative approaches to emission control.
Accordingly, there is a need for alternative methods of converting automotive emissions not utilizing conventional additional, pre-fabricated, non-regenerable solid catalytic material-containing supports in the exhaust system of an automobile.
U.S. Pat. Nos. 4,295,816, 4,382,017 and 4,475,483 describe catalyst solutions and delivery systems for improving the efficiency of combustion chambers. The catalyst solutions described in U.S. Pat. No. 4,382,017 comprise a single metal catalyst compound, H.sub.2 PtCl.sub.6.6H.sub.2 O; a chloride compound such as HCl, LiCl, or NaCl; an antifreeze compound such as ethylene glycol; and approximately 50 percent water by volume. The chloride is a blocking agent which prevents precipitation and destruction of the platinum compound which is said would otherwise occur by use of the antifreeze compound. The solutions are not taught or suggested for use in aiding conversion of automotive emissions, require the chloride "blocking agent," and contain undesirably high levels of water.
U.S. Pat. No. 4,295,816 describes a catalyst delivery system including a single platinum group metal catalyst in water. A layer of oil containing a manganese catalyst is provided on top of the surface of the water. Air is bubbled through the water and is said to meter minute amounts of catalyst to a combustion system, where the catalyst is consumed in the combustion reaction. The patent does not teach or suggest use of a solvent such as a glycol derivative, or that the solution would contain desirable viscosity and other characteristics to permit entrainment of metal compounds upon passing air over the solution, or that the solution could be used for deposition onto a surface within the exhaust system of an automobile. The patent does not teach or suggest conversion of emissions from combustion chambers.
U.S. Pat. No. 4,475,483 describes a catalyst delivery system similar to that described in U.S. Pat. No. 4,295,816, with a single rhenium metal catalyst used in place of a platinum group metal catalyst in the water. The patent further describes that an antifreeze agent such as a glycol, dissolved the water along with the catalyst. The patent teaches that if an antifreeze agent is employed, a blocking agent such as NaCl, HCl, or LiCl must be employed to prevent precipitation of the catalyst. The patent does not teach or suggest conversion of emissions from a combustion chamber.